In the field of light emitting diodes (LEDs) which are one type of semiconductor light emitting devices, vigorous researches have recently been conducted to use white LEDs for lighting, as white LEDs with higher luminance have been developed. Having a feature of point light sources, LEDs are particularly expected to replace halogen lamps and the like that are conventionally used as spotlighting at shops, museums, and showrooms.
A white LED that is widely used at present includes a combination of a blue LED chip emitting blue light and a phosphor (e.g Ce:YAG) which is excited by the blue light to emit yellow light.
A color temperature of this white LED is 4000K at lowest because of a shortage of red components. Accordingly, the white LED is not suitable as an alternative light source for halogen lamps, which have a color temperature of 3000K.
The following part lists white LEDs which have sufficient red components and are known to be potentially able to realize a color temperature of 3000K or lower.
(1) A white LED including a combination of a purple LED chip (wavelength: 380 nm to 410 nm) and blue, green and red phosphors (e.g. Japanese unexamined patent application publication No. 2002-188084)
(2) A white LED including a combination of an ultraviolet LED chip (wavelength: less than 380 nm) and blue, green and red phosphors
(3) A white LED including a combination of a blue LED chip and green and red phosphors (e.g. Japanese unexamined patent application publication No. 2002-60747)
(4) A white LED including a combination of blue, green and red LED chips (e.g. Japanese unexamined patent application publication No. H09-64420)
(5) A white LED including a combination of blue and red LED chips and a green phosphor (e.g. Japanese unexamined patent application publication No. 2000-223745)
Of the white LEDs (1) to (5), the white LEDs (1) to (3) each include a red phosphor. Since a red phosphor only has a low color conversion efficiency, these white LEDs have not yet been put into practical use in any technical fields.
The white LEDs (4) and (5) include a combination of LED chips which emit light of different colors. These white LEDs have not yet been put into practical use for lighting because of large unevenness of color that is caused for the following reason. The LED chips are generally mounted on a printed-wiring board in the white LEDs. On the printed-wiring board, the LED chips are inevitably arranged at large intervals, due to technical constraints in forming a wiring pattern by etching. As a result, the colors of light emitted from the LED chips do not mix together well.
To solve this problem, the printed-wiring board may be replaced with, for example, an SiC substrate which has a wiring pattern formed in a wafer fabrication process and can achieve high-density mounting. Even if such an SiC substrate is employed, however, a step of mounting all of the LED chips is still required.
It is not only white LEDs which have the above-mentioned problem of unevenness of color. This problem is common to all other types of semiconductor light emitting devices that combine light emitting members emitting light of different colors to emit light of a desired color.
In view of this problem, a first object of the present invention is to provide a semiconductor light emitting device that includes a combination of light emitting members emitting light of different colors and can achieve both less unevenness of color and higher productivity.
A second object of the present invention is to provide a light emitting module and a lighting apparatus using the above semiconductor light emitting device.